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Bell's Palsy (Idiopathic Facial Nerve Palsy)

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Definition & Diagnostic Criteria

1. Paralysis or paresis of all muscle groups on one side of the face
2. Sudden onset
3. Absence of signs of CNS disease
4. Absence of signs of ear or cerebellopontine angle disease

"All that palsies are not Bell" — approximately 30–40% of facial palsies have an identifiable alternative cause.

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Epidemiology

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Anatomy & Lesion Localization

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Etiology & Pathogenesis

• HSV-1 DNA has been identified in geniculate ganglion tissue of autopsy specimens
• Murakami et al. detected HSV DNA by PCR in endoneurial fluid of Bell's palsy patients (not in controls)
• There is no seasonal clustering, supporting reactivation rather than new infection
• VZV reactivation is also implicated (and, when vesicles are present, defines Ramsay Hunt syndrome)
• Proposed mechanism: viral neuropathy → oedema → ischaemic compression within the bony facial canal

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Clinical Features

• Hypesthesia/dysesthesia of CN V or IX — 80%
• Hyperacusis (stapedius dysfunction) — up to 30%
• Retroauricular or facial pain
• Taste disturbance (chorda tympani)
• Reduced lacrimation (greater petrosal nerve)
• Vagal motor weakness — 20%

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Differential Diagnosis

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Investigations

• Clinical diagnosis in typical cases; no routine imaging needed
• Electroneuronography (ENoG): predicts prognosis — >90% degeneration by days 3–14 is a poor prognostic sign
• Schirmer test (lacrimation), stapedial reflex, taste testing — topographic localization (limited accuracy)
• MRI with gadolinium if atypical, progressive, or recurrent — enhancing facial nerve can be seen
• If bilateral: CXR + serum ACE (sarcoidosis), Lyme serology

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Treatment

1. Corticosteroids ✅ (First-line)

2. Antivirals ⚠️ (Adjunct)

3. Eye Protection 👁️ (Essential)

• Lubricating eye drops (artificial tears) during the day
• Eye ointment and patching at night
• Critical if CN V sensation is also impaired (neurotrophic risk)

4. Physical Therapy

• Neuromuscular re-education, facial exercises, and mirror biofeedback
• Systematic reviews (Nakano et al., 2024 [PMID 37149416]; Varelas et al., 2025 [PMID 39647183]) suggest benefit for recovery and reduction of sequelae

5. Surgical Decompression ❌

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Prognosis

• ~70% of patients recover completely without treatment
• 30% have incomplete paralysis at onset → nearly all recover fully
• Of those with complete paralysis: ~70% still recover fully; ~15% have permanent sequelae
• Poor prognostic factors: complete paralysis, age >60, diabetes, hypertension, severe pain, >90% ENoG degeneration
• Sequelae of aberrant regeneration:
  • Synkinesis (involuntary eye closure with mouth movement)
  • Crocodile tears (lacrimation while eating — gustatory tearing)
  • Contracture of facial muscles

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Ramsay Hunt Syndrome (Distinguish!)

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Recent Evidence

• A 2023 meta-analysis (PMID 37103913, JAMA Otolaryngol) found a small but significant association between SARS-CoV-2 vaccination/infection and Bell's palsy
• Laser therapy has emerging evidence (PMID 39546047, 2024) but is not yet standard of care
• Physical therapy meta-analyses support facial exercises as adjuncts to pharmacotherapy

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Facial Nerve (CN VII) — Complete Overview

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1. Fiber Components of CN VII

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2. Course of the Facial Nerve — Six Segments

Key anatomical notes:

• The intrapontine fibers loop dorsally around the abducens nucleus → form the facial colliculus on the floor of the 4th ventricle (explains CN VI + VII palsy together in pontine lesions)
• Enters IAC together with CN VIII
• The geniculate ganglion (at the genu) carries sensory cell bodies and gives off the greater petrosal nerve

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3. Branches and Their Functions

Intratemporal Branches

Extratemporal Branches (mnemonic: To Zanzibar By Motor Car)

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4. Levels of Lesions and Their Features

Mnemonic for lesion levels ascending from stylomastoid foramen: "Some Lovers Go Home Crying" Stylomastoid → taste Loss → Hyperacusis → Greater petrosal (lacrimation) → Cortex

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5. UMN vs. LMN Facial Palsy — Key Distinction

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6. Treatment of Bell's Palsy

A. Corticosteroids (First-line — Grade A evidence)

• Prednisolone 60–80 mg/day × 7 days, then taper over 7 days (alternative: 25 mg twice daily × 10 days)
• Must start within 48–72 hours of onset
• Increases complete recovery from ~63% → ~83% at 3 months
• Mechanism: reduces inflammatory oedema within the bony facial canal

B. Antivirals (Adjunct to steroids)

• Acyclovir 400 mg 5× daily × 7–10 days, or valaciclovir 1g TDS × 7 days
• Antiviral alone = no benefit
• Steroids + antivirals = added benefit in reducing long-term sequelae (synkinesis, crocodile tears)
• Especially indicated in severe/complete palsy and Ramsay Hunt syndrome

C. Eye (Corneal) Protection — Essential

• Artificial tear drops during the day
• Lubricating ointment + eye patch at night
• Critical to prevent exposure keratopathy (risk is greatest when CN V sensation is also reduced)

D. Physical Therapy

• Facial neuromuscular re-education, exercises, mirror biofeedback
• Useful as adjunct; recent meta-analyses support benefit in recovery and synkinesis prevention

E. Surgical Decompression

• Not recommended in routine Bell's palsy
• No RCT evidence of benefit
• May be considered by specialists in selected cases with >90% degeneration on ENoG within 14 days

Summary Algorithm

Onset ≤72 hrs?
    ├── YES → Prednisolone + Acyclovir + Eye care
    └── Severe/Complete palsy → definitely add antivirals
         ├── ENoG at day 3–14 if no recovery
         └── >90% degeneration → specialist referral

Prognosis

• ~70% recover completely without treatment
• Treatment improves this to ~83%
• ~10% have permanent sequelae
• Sequelae of aberrant regeneration: synkinesis (jaw winking), crocodile tears (gustatory tearing), facial contracture

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